Preheat Oven to 225°F. In a small bowl, combine diced strawberries and granulated sugar and set aside.
Spread Nutella on 4 slices of bread and top with other 4 slices, creating 4 sandwiches.
In a shallow baking dish, whisk the milk, eggs, vanilla and cinnamon until combined. Working with two at a time, dip sandwiches into egg mixture to soak all sides. Heat a 12-inch greased nonstick skillet on medium. Add dipped sandwiches and cook 2–3 min. per side, until deep golden brown. Transfer to oven to keep warm. Cook remaining 2 sandwiches.
Slice each sandwich down the middle and top with strawberries and powdered sugar.